The ink jet recording method is a printing method in which droplets of an ink are allowed to fly and adhered to a recording medium such as paper to perform printing. With recent innovative improvements in inkjet recording technology, the inkjet recording method has also been applied in the field of high-definition printing which has hitherto been achieved only by silver halide photography and offset printing. The ink jet printing has been made not only to plain paper, but also to glossy paper having high glossiness such as photographic printing paper or art paper.
A water-soluble dye has hitherto been often used as a coloring agent in an ink composition used in the ink jet recording method. A water-soluble dye ink can also be printed on various recording media, and excellent glossiness can be obtained in recording onto glossy paper. On the other hand, however, the aqueous dye ink has the drawback of being poor in light resistance, gas resistance and water resistance, so that the use of a pigment as the coloring agent has been studied in recent ink development.
An aqueous pigment ink is a dispersion in which fine pigment particles having a definite particle size have been uniformly dispersed in a water solvent, and an ink film containing the pigment is formed on a recording medium after printing on the recording medium. Accordingly, it exhibits excellent color developing properties on various recording media, particularly on plain paper. However, when it is printed on a recording medium whose surface is smoothly treated, such as glossy paper, there has been the problem of impairing glossiness of a recorded area by diffused reflection of light due to the fine pigment particles in the ink film. Further, in order to improve glossiness of the recorded area, various gloss imparting agents are allowed to be contained in the ink composition in some cases. However, there have been the problems of deteriorated storage stability of the ink composition, deteriorated print stability and decreased print density on plain paper.
To such problems, JP-A-2004-75988 (patent document 1) proposes a pigment ink in which a water dispersion of a fine water-insoluble vinyl polymer particles is used, whereby printing high in color development and excellent in glossiness is possible. However, in the ink composition using the above-mentioned water dispersion, the ink composition excellent in color developing properties on plain paper is deteriorated in glossiness on glossy paper, and conversely, the ink composition excellent in glossiness on glossy paper is deteriorated in color developing properties on plain paper. Thus, there has been the problem of failing to sufficiently satisfy high color developing properties and high glossiness at the same time by one ink composition. An ink composition having both of high color developing properties to plain paper and high glossiness to glossy paper at the same time while satisfying storage stability of the ink composition and print stability has not been obtained yet.
Patent Document 1: JP-A-2004-75988